The method of preparation of the cytoplasmic inhibitor of neutral ribonuclease activity from pork liver will be developed to provide a convenient source for the routine preparation of the protein. This procedure is designed to be used for commercial production which will render the inhibitor more widely available for use in improving the yields of proteins synthesized in in vitro translation experiments and in the synthesis of complementary DNA by reverse transcriptase. Structural studies on the RNase inhibitor, including the role of the -SH groups, will concern the possibility that low intracellular -SH concentrations can lead to inactivation of the inhibitor in vivo, with particular reference to muscular dystrophy in the mouse. Research on the cellular uptake of dimeric ribonuclease and glycosylated derivatives thereof will be continued both in terms of the inherent cytotoxicity of the enzyme and its use as a carrier of tumorostatic drugs or antimalarial agents to the liver. Search for the physiological role of 2', 3'-cyclic nucleotide 3'-phosphohydrolase in the nervous system, an enzyme which has now been isolated in purified form from both brain white matter and retina, will concern the question of whether the two protein moieties of m.w. ca. 44,000 in the isolated enzyme are individually catalytic activity.